Kirby and Bowser have good matchups vs MK (by good I mean compared to most of the cast). I'm also convinced that DK goes 45:55 against MK (this is one of my favorite matchups when I'm playing DK). I think a good handful of MK's matchups are gonna wind up to even or very close to even in the future.
I agree...Falco, Snake, Wario, Bowser, Kirby and Diddy look 5/5ish to me. Zamus and G&W are very close, some people also like to mention Olimar though I'm not sure yet.
I think most characters can beat MK. My impression is that a 4/6 in the opponents favour is still a realistically managable match-up...that means that Snake, Falco, D3, G&W, ROB, Marth, Diddy, Lucario, Peach, Kirby, DK, Olimar, Zamus and Wario have realistic chances to win. I'm also adamantly insistent on Luigi having a 4/6 match-up as well as Wolf.
Most people who have troubles with MK should play him a little. It really helps you to find ways to deal with him and it's not as hard as most people think. It's not easy though but sooner or later you'll find out ways to beat him. D3, Falco and Snake **** most characters
much harder anyways. There are few cases where MK is actually a characters worst match-up.
No need for a new stage rule. There are very few stages that are more beneficial for MK than most other characters. Lylat is the only stage I can think of but you can just ban it. People overrate MKs "immunity" to get CPed. He gets KOd very fast on flat stages like Brinstar or Halberd and has KO issues on FD. All grab release CGs are 0-deaths on Delphino Plaza and Castle Siege....5 potential CPs against Meta for many characters. MK on the other hand barely benefits from other stages than Lylat Cruise in the first place so I think he's easier to CP than King Dedede (or Snake) imo...